A front-page headline Sunday incorrectly described the weapons testing work under way at Lawrence Livermore Laboratory. The lab conducts testing on high explosives, which are non-nuclear and create the initial explosion in the chain of events leading to a nuclear detonation. There has never been testing at Lawrence Livermore Laboratory that leads to a nuclear detonation.

Researchers said Sunday the mass die-off occurred because unusually large amounts of sea ice forced penguin parents to travel farther in search of food for their young. By the time they returned, only two out of thousands of chicks had survived.